Transition metal complexes absorption spectra

Transitions between different electronic states result in absorption of energy in the ultraviolet, visible and, for many transition metal complexes, the near infrared region of the electromagnetic spectrum. Spectroscopic methods that probe these electronic transitions can, in favourable conditions, provide detailed information on the electronic and magnetic properties of both the metal ion and its ligands. 

The electronic spectrum is yet another property which illustrates the similarities between the metallocenes and (7r-ollyl) metal compounds. In Table VI are listed some data for a series of Coin(absorption bands with the small extinction coefficients are probably two of the spin-allowed d-d transitions. Scott (34) has developed an approximate axial ligand field model for the carborane-transition metal complexes and has discussed the optical spectra in relation to this bonding theory. The actual assessment of bonding in the (7r-ollyl) metal compound as well as the metallocenes would be greatly aided by accurate assignments of the electronic spectra. 

Figure 5a shows CD spectra of tartaric acid, which has an absorption i the short wavelength region and thus is prone to suffer from dispersion effect as compared with transition metal complexes. Two solution spectra in solvent of different polarity, water and dioxane, are similar to each other, but the CD C a nujol mull is quite different from that in solution. A KBr disc prepared t avoid dispersion effects gave a solid-state tartaric acid spectrum similar to thi in solution (Fig. 5b). Thus the difference between the nujol mull CD and solutid CD is not due to the different molecular conformation or intermolecular intera tion in the two phases. Most likely, it is due to the dispersion effect in the cas of the nujol mull form. Many nujol mull CD spectra of organic compound have been reported recently, but most of them appear to suffer from substanth dispersion effects. It is to be noted that the dispersion terms for molecules C...

The visible-UV absorption spectrum of transition metal complexes is characterized by a high density of various... 

Acetonitrile is a convenient solvent in which to study, by pulse radiolysis, the one-electron reduction of transition metal complexes that are not stable in water or hy-droxylic media. For example, the tantalum compound [Ta2Cl6(4-methylpyridine)4] has been shown to be reduced by CH3CN with A = 1.2 x 10 dm mol s [24], The absorption spectrum of the product shows the characteristic features of d-d transitions and it was suggested that the added electron is delocalized over the double-bonded Ta=Ta moiety. Another example is the radiolytic reduction of the vanadium(III) complex [VCl3(y-pic)3], where y-pic is 4-methylpyridine, to the derivative via the V complex [25]. It was shown by pulse radiolysis that the electron adduct of the complex decayed in a first-order process with k= 1.3 x 10 s which is thought to involve loss of Cl". The intermediate V complex had a... 

Crystal field theory was developed, in part, to explain the colors of transition-metal complexes. It was not completely successful, however. Its failure to predict trends in the optical absorption of a series of related compounds stimulated the development of ligand field and molecular orbital theories and their application in coordination chemistry. The colors of coordination complexes are due to the excitation of the d electrons from filled to empty d orbitals d-d transitions). In octahedral complexes, the electrons are excited from occupied t2g levels to empty Cg levels. The crystal field splitting Ao is measured directly from the optical absorption spectrum of the complex. The wavelength of the strongest absorption is called Amax and it is related to Ao as follows. E = hv, so Ao = hv = Because en-... 

The visible-UV absorption spectrum of transition metal complexes is characterized by a high density of various electronic excited states (Metal-Centred, Metal-to-Ligand-Charge-Transfer, Ligand-to-Ligand-Charge-Trans-... 

There followed many other exciting adventures involving studies of the infrared spectra of transition-metal complexes, but I will mention just one which I find particularly memorable. This followed the discovery by Bernard Shaw of a remarkably stable volatile platinum complex produced by reduction of [PtCl2(PEt3)2], the spectrum of which had a very strong and sharp absorption band near 2200 cm ... 

In this review, we explain the SAC-CI applications to molecular spectroscopy with some examples. In Section 2, we briefly explain the theoretical and computational aspects of the SAC-CI method. Then, we show some SAC-CI applications to molecular spectroscopy the excitation and ionization spectra of tt-conjugated organic molecules (Section 3), collision-induced absorption spectra of van der Waals complex (Section 4), excitation spectra and NMR chemical shifts of transition metal complexes (Section 5), photofragmentation reaction of Ni(CO)4 (Section 6), absorption spectrum of free-base phthalocyanine (FBPc) and bacterial photosynthetic reaction center... 

The incorporation of anionic transition-metal complexes into PPy has enabled a range of spectroscopic techniques to be employed (UV-visible, EPR and Mossbauer spectroscopy) which have provided information about the counter-anion s structure and local environment. A relationship is apparent between the room-temperature conductivity and the position of the absorption maximum in the 300-500 nm region of the UV-visible spectrum. The conjugation length of the bipolarons seems to be an important factor that... 

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